1. Field of the Invention
The present invention relates to a heat treatment apparatus including a hot plate portion for heat treatment of a substrate such as a semiconductor wafer to which a coating liquid is applied and a cooling plate for transferring the substrate that has been subjected to heat treatment, as well as to a heat treatment method.
2. Description of the Background Art
A coating and development apparatus for applying a resist to a substrate and developing the exposed substrate has been used as an apparatus for forming a resist pattern on a substrate such as a semiconductor wafer (hereinafter, referred to as a wafer) or a glass substrate for an LCD (liquid crystal display). In the apparatus, a heat treatment apparatus referred to, for example, as a baking apparatus, is incorporated. In an apparatus for heating the substrate to which a resist liquid is applied, for example, the heat treatment apparatus serves to dry a solvent in the resist liquid, while in an apparatus for heating the substrate after exposure using a chemically amplified resist, the heat treatment apparatus serves to diffuse acid in the resist.
FIG. 18 shows an exemplary structure of a heat treatment apparatus 100. In heat treatment apparatus 100, a cooling plate 104 and a heat treatment portion having wafer elevation mechanisms 106 and 107 respectively are provided. Cooling plate 104 is movable between a position (home position) shown in the drawing and a position above a hot plate 108, by means of a not-shown drive mechanism.
A substrate such as a wafer W transferred from a transfer port 109 into heat treatment apparatus 100 by a not-shown transfer mechanism moves to a position above hot plate 108 by means of cooling plate 104, and placed on hot plate 108. Thereafter, wafer W is subjected to prescribed heat treatment on hot plate 108, and then returns to the home position by means of cooling plate 104. Wafer W is cooled until it is unloaded from heat treatment apparatus 100 by the not-shown wafer W transfer mechanism, for example for 30 seconds.
In conventional heat treatment apparatus 100, in cooling the wafer placed on cooling plate 104, a cooling mechanism such as a Peltier element or a cooling pipe through which a coolant passes has been provided inside or under cooling plate 104. Accordingly, heat treatment apparatus 100 tends to be bulky and maintenance work is complicated. The present inventors have been studying cooling of wafer W by using only the cooling plate, without providing the cooling mechanism as described above.
Meanwhile, with the tendency toward higher throughput in recent years, necessity for reducing a time required for heat treatment per one wafer W has grown. As the time for heating wafer W is required for such a process as drying of the solvent in the resist liquid, it is impossible to reduce such a time. Accordingly, further reduction in the time for cooling wafer W has been demanded. If the cooling mechanism as described above is not provided, however, cooling of cooling plate 104 after cooling of wafer W is not satisfactory, and a temperature of cooling plate 104 gradually increases with the increase in the number of wafers W that are successively treated. Therefore, capability of cooling plate 104 for cooling wafer W becomes insufficient, and the temperature of wafer W is gradually raised with the increase in the number of wafers to be treated. The temperature of cooling plate 104 and the temperature of wafer W tend to be constant as wafers W are successively subjected to heat treatment, however, several to several tens of wafers W have been subjected to heat treatment by that time. Then, difference in a cooled state between wafers W is caused, which results in variation in thickness of a resist film or a pattern among wafers W.
In addition, in spite of provision of a cooling mechanism, if cooling capability thereof is low, similar problem arises. In such a case, capability in cooling cooling plate 104 should be enhanced, for example, by increasing the number of Peltier elements or making a coolant circulating pump or a chiller greater in size.
Japanese Patent Laying-Open No. 2003-347305 describes the technique to increase heater output at the time when a substrate is loaded in a treatment chamber, in order to suppress drawbacks such as lowering in a temperature in the treatment chamber due to initial loading of several substrates into the treatment chamber in successive treatment of the substrate. If the technique described in Japanese Patent Laying-Open No. 2003-347305 is applied to cooling plate 104 described above, the cooling mechanism for cooling cooling plate 104 is required and high cooling capability is required in the cooling mechanism.